The invention relates to a method for the manufacture of contact lenses, especially a method for the one-step manufacture of contact lenses that largely do not have to be finished, by direct polymerization of a polymerization batch in a mould, according to the precharacterising clause of patent claim 1. "Polymerization batch" is to be understood hereinafter as meaning, quite generally, polymerizable monomers, polymerizable oligomers, polymerizable prepolymers or polymerizable mixtures thereof.
Recently, many attempts have been made to manufacture contact lenses in a so-called one-step shaping process by direct polymerization of a polymerization batch in a mould. In contrast to the original methods of manufacture in which the front and/or the rear face of the contact lens are/is produced on a contact lens button by removing material, in this one-step method the front face and the rear face of the contact lens are determined only by the corresponding shaping faces of the mould. The aim of this so-called one-step method is to manufacture contact lenses that largely do not have to be finished, by direct polymerization of a polymerization batch inside the mould. Usually the moulds are made of plastics and are in the form of disposable moulds. Each mould is accordingly used for the manufacture of only a single contact lens. Methods of manufacture that use a separate disposable mould for each lens to be produced are described, for example, in FR-A-1,462,519 or in U.S. Patent Specifications U.S. Pat. No. 3,871,803, U.S. Pat. No. 3,614,624 and U.S. Pat. No. 4,455,893. Finally, in the method described in U.S. Pat. No. 4,254,065, so-called "raw buttons" are manufactured by injection-moulding in moulding tools. The production of the actual customer-specific lenses is effected by finishing the prefabricated raw buttons by removing material.
A large number of preparatory operations precede the actual process of manufacturing the contact lens. For example, shaping tools for the manufacture of the moulds are produced in accordance with the desired parameters of the later contact lens, such as, for example, lens diameter, curvature of the rear face and focal power of the lens. Those shaping tools, which are normally produced from metal, are then fitted in so-called mould plates which are in turn inserted into an injection-moulding tool. Each shaping tool is thus used for the manufacture of some ten thousand disposable plastics moulds before it is rendered unusable by the great mechanical stresses of that injection-moulding process and the stringent accuracy requirements. Each of the disposable moulds produced in that manner is then used for the manufacture of a single contact lens. After any necessary after-treatment of the contact lens, for example a tinting of the contact lens or a hydration of so-called soft contact lens material, which preferably takes place in the associated mould, the contact lens is advantageously packed, still in its associated mould (half), and stored or despatched. The totality of all those process steps is referred to as full-mould technology. The individual process steps are given again below in summary:
(1) Manufacture of the shaping tools PA0 (2) Fitting of the shaping tools in mould plates PA0 (3) Insertion of the mould plates into an injection-moulding tool PA0 (4) Injection-moulding of the disposable plastics moulds PA0 (5) Manufacture of the contact lens by direct polymerization of the polymerization batch in the disposable mould PA0 (6) After-treatment of the contact lens if necessary PA0 (7) Packing of the contact lens in disposable mould
Full-mould technology has proved to be especially advantageous and economical in particular for the production of soft contact lenses, for example those which contain poly-2-hydroxyethyl methacrylate (P-HEMA) or copolymers of that compound. Soft contact lenses are manufactured in relatively large production runs. In particular, however, owing to their very good fitting properties in respect of the shape of the eye, especially the geometric nature of the cornea, a relatively small number of sets of parameters (for example lens diameter and curvature of the rear face of the lens) is sufficient to cover a wide range of fittings in cases of sight defects. Full-mould technology has therefore been successful especially for the manufacture of soft contact lenses since the costs and time required for the preparatory operations listed under process steps (1) to (4) prove to be proportionately very low owing to the relatively small number of different shaping tools required and the large contact lens production runs per shaping tool.
A second large group of contact lenses is the so-called hard contact lenses and the so-called hard/flexible contact lenses. For example, contact lenses made of polymethyl methacrylate (PMMA) are referred to as hard contact lenses; hard/flexible or Rigid Gas-Permeable (RGP) contact lenses are preferably manufactured from materials having a high degree of oxygen permeability, for example from fluorine- and/or silicone-containing polymers. Owing to the relatively high degree of rigidity of those materials, hard and hard/flexible contact lenses fit the geometry of the cornea of the eye to only a limited extent. However, in order to make those contact lenses too as comfortable as possible to wear, without irritation to the eye and without pressure, while achieving optimum optical correction of the sight defect, in particular the curvature of the rear face of the lens and its diameter are matched as accurately as possible to the surface shape and curvature of the cornea and to the diameter of the pupil of the eye of the contact lens wearer. Together with the multiplicity of different focal powers required for the contact lenses, there result a large number of different contact lenses having up to 4000 or more different parameter values in respect of the contact lens diameter, the curvature of the rear face of the contact lens--the face that rests on the cornea--and the focal power of the contact lens. Only very small production runs, however, result therefrom for the individual combinations of parameters. For that reason, hard and hard/flexible contact lenses have hitherto been manufactured mainly by material-removing shaping from lens buttons. The fluorine- and/or silicone-containing polymers particularly are, however, often difficult to machine by cutting processes, which markedly increases the manufacturing time and the manufacturing costs of such lenses. In addition, the contact lens is relatively awkward to handle when it is being machined. Care must particularly be taken that the already produced front or rear face of the contact lens is not damaged when the second lens face is machined. Furthermore, during machine-cutting, stresses often also occur in the contact lens material which can sometimes lead even to the destruction of the contact lens.
There is accordingly a desire to provide a method for the manufacture of contact lenses that permits an economical use of full-mould technology even in the case of types of contact lens that are manufactured in numerous different parameters and accordingly in small production runs. In addition, the method is also to permit a simple, rapid and inexpensive manufacture of contact lenses from contact lens materials that are difficult or impossible to machine by cutting. The above-mentioned disadvantages that often occur when the contact lenses are machined are also to be largely avoided.